Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 090351

Area Forecast Discussion
National Weather Service Salt Lake City UT
851 PM MST Fri Dec 8 2017

.SYNOPSIS...Strong high pressure will remain in place through at
least the middle of next week.


.DISCUSSION...A high amplitude mid level ridge encompasses much
of the western CONUS this evening. This ridge remains centered to
the west of the forecast area across the central Sierras, inducing
a light northerly flow aloft. As the ridge has build east over
the past 24 hours, warming aloft has helped to slowly strengthen
inversions across northern and central Utah, however a relatively
mild and dry airmass has allowed some mixing within the lowest
100mb or so. As such, although haze has been on the increase with
a gradual decline in air quality along the Wasatch Front, the
trends have not been as severe as we typically see with colder,
stronger inversions involving snowpack or very cold
canadian/arctic air. Sheltered locations such as the Cache Valley
remain entrenched in a much colder, stronger inversion, and areas
of fog are likely to redevelop overnight.

Little change is expected through at least the first half of the
week before the mid level ridge begins to retrograde westward.
This will open the door for shortwave features digging down the
eastern periphery of this ridge. The EC does drop a shortwave
south through the forecast area midweek, however confidence is
quite low this will actually evolve as currently forecast.
Assuming this wave digs well east of the area, the first real
opportunity to mix out the stagnant valley airmasses looks to
come late in the week, when the EC and Canadian have been fairly
consistently advertising a shortwave trough and attendant cold
front digging through the forecast area, with GFS bringing this
feature through about a day later. In the meantime, will likely
see an increase in haze and decrease in air quality during the
early to mid week period.


.AVIATION...Light southeasterly winds and VFR conditions will
prevail through the overnight period at KSLC, with a 20 percent
chance of visibility falling into the MVFR range at times. Winds
may also occasionally become light and variable.





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